This invention relates to a method for increasing the productivity of olefin polymerization catalysts and to the production of such a catalyst which exhibits better productivity and produces a polymer with acceptable stereospecificity. More particularly, the invention relates to an improved method for washing an aluminum chloride co-crystallized titanium halide and adding an electron donor to increase the productivity of the catalyst.
U.S. Pat. No. 4,048,415, issued Sept. 13, 1977, discloses an improved process for the polymerization of olefins with a catalyst which has a titanium tetrachloride component prepared by reduction of titanium tetrachloride with hydrogen, silicon, metallic titanium or metallic aluminum, a complex of aluminum chloride with an electron donor, and a polysiloxane, and extracting the complex from the catalyst with a saturated hydrocarbon. The patentee desires to remove the complex, aluminum chloride, and electron donor which the patentee states are detrimental to the polymerization. I have found that better catalyst productivity can be obtained without sacrificing stereospecificity if the catalyst is washed with an olefin rather than a saturated hydrocarbon. Furthermore, addition of the electron donor improves the productivity of the catalyst.
U.S. Pat. No. 3,404,096, issued Oct. 1, 1968, discloses a method for improving a titanium trichloride catalyst by pretreating the catalyst in an inert diluent in the absence of an activator with an olefin having 2 to 6 carbon atoms for a minimum of about 10 minutes. It is said that the catalyst undergoes a physical change whereby it agglomerates into curds and appears to swell. Defensive Publication T951,009, published Oct. 5, 1976, discloses an olefin polymerization catalyst which comprises titanium trichloride ground together with octamethylphyrophosphoramide wherein the two components are ground together in a ball mill and then contacted with propylene for a time sufficient for from 0.1 up to 5.0 moles of propylene to be taken up by the titanium compound. Both of the above catalysts are different from the catalyst of the present invention in that they both appear to react with the olefin such that material is added to the catalyst and there is no addition of electron donor with, the olefin treatment.
My co-pending application entitled Improved Olefin Polymerization Catalyst Activity by Olefin Washing and Readdition of Electron Donor, Ser. No. 530,497, filed Sept. 9, 1983 and now Pat. No. 4,471,064, discloses a method for increasing the productivity of an olefin polymerization catalyst containing an aluminum chloride co-crystallized titanium halide modified with an electron donor containing an ester group which comprises washing the modified titanium halide with an olefin and then adding back electron donor thereto. Thus, it is a two-step process. Surprisingly, I have found that many of the advantages of the above process can be obtained if the olefin washing and the adding of electron donor are carried out simultaneously. Even though it would seem that the two steps would interfere with one another, a polymerization catalyst with improved productivity can be obtained without the necessity of expensive and time consuming milling of the catalyst with the electron donor.